The present invention relates to an injection molding machine including at least an injection molding unit having a plurality of actuating electrical servomotors.
The injection molding units of this type have a modular structure formed of a plurality of structural subunits. An injection molding unit of this type is disclosed in German Publication P42 20 445.3. The injection molding unit disclosed in P42 20 445.3 includes the following subunits:
a first subunit that consists of a plastifying block formed of an extrusion cylinder and a screw rotatably supported therein; PA1 a second subunit that consists of a metering drive for the screw of the plastifying block; PA1 a third subunit that consists of two parallel drives for effecting displacement of an injection nozzle of the plastifying block between the plastifying block and a mold; and PA1 a fourth subunit that consists likewise of two parallel drives for effecting injection displacement of the screw of the plastifying unit in the extrusion cylinder, that is, for effecting axial displacement of the screw.
In the injection molding unit of German Publication P42 20 445.3, the plastifying block is located between the pairs of drives forming the third and fourth subunits.
In order to reduce the energy costs associated with driving different components of the injection molding unit and to provide a compact structure, at least the drive pair forming the fourth subunit is formed of electrical servomotors provided with forced cooling, in particular, liquid cooling, with the two electrical servomotors being connected for synchronous operation. Also, advantageously, in addition to the electrical servomotors forming the fourth subunit, the drives of the second and third subunits are also formed of liquid-cooled electrical servomotors.
The use of liquid-cooled electrical servomotors in the injection molding unit of German Publication P42 20 445.3 insures precise running of displacement steps and, therefore, of the injection process. As a result, the quality of the produced workpieces can be substantially increased. Furthermore, the total costs associated with the manufacturing of an injection molding machine are substantially reduced. Also, separate electrical servomotors can directly be fed from the available electrical main.
However, of particular importance is providing with liquid-cooled electrical servomotors, the components for injection molding machines, which are to be operated under "clean room" conditions. The heat energy, which is carried away by the cooling medium from the region of a drive, has no effect on the "clean room" conditions. The heat energy, which is carried away, can subsequently be reused, e.g., for tempering the mold and/or the heating bands of the extrusion cylinder of the injection molding unit. As a result, the overall efficiency of the injection molding machine is substantially increased, while the energy costs, associated with the operation of the injection molding machine, are reduced.
When three-phase electromotors are used as liquid-cooled electrical servomotors, the drive system of the injection molding unit includes, as a rule, power and control electronics or electronic units for each of the three-phase servomotors. Such power and control units may be formed as a semiconductor convertor having a modular structure, formed of one or several power and control units connected by an intermediate circuit to a base unit. In such a modular structure, the intermediate circuit is connected to an electrical main through a transformer and an input rectifier.
A power and control unit provides for a rotary field with variable frequency, amplitude and phase position, dependent on the rotational speed and the load of a respective electrical servomotor. Naturally, with the use of such power and control units, not insignificant energy losses occur, which are converted, in an undesirable way, into heat energy. As a result, when such power and control units are used in an injection molding machine, they may adversely effect the "clean room" conditions as well as reduce the total efficiency of the injection molding machine.
Accordingly, an object of the invention is to provide an injection molding machine of the type, which is described above, in which the above-discussed drawbacks, associated with the use of the power and control electronic units, are eliminated.